The present invention relates in general to autogyros, and more particularly to autogyros having an airframe and the usual main propulsive engine and pusher propeller, and a lifting rotor provided with an auxiliary rotor drive in the form of a mechanical power takeoff from the main propulsive engine and a hydraulic transmission system for tapping a minor portion of power from the main engine and transmitting it to the rotor.
Autogyro type aircraft became almost extinct after the advent of helicopters in the 1940's. With autogyro rotors unpowered in flight, they were unable to hover and thus were less versatile than helicopters, but they are mechanically simpler and less expensive than helicopters. In flight operations where hovering capacity is not required, autogyros may still be preferred to helicopters and airplanes. Considerable amount of success has been achieved in the past to make autogyros more competitive to helicopters, especially in the area of giving more vertical takeoff capability. One of the efforts to give autogyros a vertical takeoff capability was the "jump takeoff" development, wherein the lift rotor was pre-rotated mechanically beyond its normal rotational speed and then simultaneously the drive was disconnected and and the collective pitch of the rotor blades increased. This produced a sudden helicopter-like downward flow of air through the rotor and enough vertical lift to "jump" the aircraft off the ground. As the speed and lift of the rotor decayed, enough forward speed was gained to continue flight with blades at reduced "autorotative" pitch without appreciable settling down. Although this "jump takeoff" development operated successfully, it failed to restore the autogyro to its earlier popularity.
Later, a new type of autogyro identified by the trade name "Gyrocopter" was developed, which retained the basic design features of the autogyro of obtaining lift from a free-running rotor whose blades were set in low "autorotative" pitch, and derived forward propulsion from a forward thrusting propeller, but was of "pusher" configuration, and its airframe was of simpler open-air skeletal construction. This aircraft lent itself to kit type marketing and construction at home by amateur hobbyists, and its popularity rapidly spread and soon exceeded that of earlier tractor types.
The present invention represents a further development to enhance operational versatility of the autogyro by equipping it with a continuous duty rotor drive. Unlike previous rotor drives which were of all-mechanical type and had fixed reduction ratio transmissions from engine to the rotor, the design of the present invention uses a compound transmission, one stage of which is hydraulic with a continuously variable speed ratio between input and output. In addition, while old style drives were disconnected before the takeoff, the proposed drive stays engaged in flight, which produces some reaction torque against the airframe, but its magnitude is small compared to helicopters and is beneficial in canceling the yaw torque produced by the propeller slipstream.
Provision of this continuous duty auxiliary rotor drive provides subtle, but nevertheless significant, advantages. Because its rotor is always driven during and after takeoff, the pilot can more accurately estimate the length of the pre-takeoff ground run, thus improving the safety of the machine in cross-country flying from unprepared fields, as well as during student training. Economy of operation is also improved, because horsepower fed directly to the rotor is spent more efficiently there than by the propeller. This permits flight at a reduced throttle and results in savings in fuel consumption. Providing for a continuous powering of the rotor by tapping a minor portion of power from the main engine also eliminates the danger of the rotor slowing down during "zero-g" pushover maneuvers, providing another important safety factor. It also provides smooth chatter-free and wear-free engagement of rotor power drive, and of rotor stopping action, by means of valves in a closed circuit hydraulic recirculating transmission.
An object of the present invention, therefore, is the provision of a novel autogyro having a continuous duty auxiliary rotor drive by providing a compound mechanical-hydraulic transmission to achieve transfer of a minor portion of power from the engine to the rotor, to achieve economy of operation, reduce length of pre-takeoff ground runs, minimize faulty operation during "zero-g" maneuvers and achieve desired flight characteristics not attainable by mere "autorotation" of the rotors from air flow rotating forces.
Another object of the present invention is the provision of an autogyro of the type described in the preceding paragraph, whrein the compound mechanical-hydraulic transmission and control system is arranged to prevent inadvertent simultaneous engagement of rotor drive and of rotor brake by combining both control operations into one, placing each function on the opposite ends of a single control movement.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings showing a preferred embodiment of the invention.